The present invention relates to marine structures which provide a platform for carrying out operations in arctic and sub-arctic regions. The marine structure of the present invention is particularly well suited for conducting exploration drilling in areas such as the Alaskan Beaufort Sea and serves equally well for supporting production equipment, liquification plants, gas compression plants, crude oil storage and offshore loading facilities in this and other such regions. Most exploration drilling in the Alaskan Beaufort Sea has occurred close to shore and often behind barrier islands in shallow water near gravel sources so that gravel islands may be utilized to serve as an exploration drilling platform. The need to use such gravel island platforms severely limits the development and exploration of areas which are further offshore and removed from convenient sources of gravel and where more severe environmental conditions are encountered.
Since in most arctic and sub-arctic locations, only about two months of acceptable weather for construction per year are available, structures designed for use in these regions should ideally require a minimum amount of construction effort at the job site. Structures adapted for use in ice laden environments must be designed to safely resist substantial ice forces encountered even when the structures are mounted upon weak bottom soils or silts. It is also desirable for such structures, particularly those used for exploration drilling, to be able to relocate from one drilling site to another on a year round basis in the event that the first drilling site proves unsuccessful. It is further desirable to provide a structure which may be developed in stages so that exploration drilling may proceed without the associated platforms need to support production equipment which may be added once the well proves to be successful.